1. Field of the Invention
The present invention relates to heat transfer apparatus and methods. It further relates to apparatus and methods for the transfer of heat from one fluid to another fluid, and more particularly to an air-heated heat exchanger for heating low-temperature fluids.
2. Description of the Related Art
Heat exchanger apparatus are well known for transferring heat from one medium to another. Heat transfer is an engineering concern in a wide range of processes and systems and is utilized in many industries, such as, for example, the generation of energy, chemical production, refining of petroleum products, air conditioning, and automotive industry, to list but a few. Heat exchangers can be classified based on their design such as, for example, shell and tube designs, double pipe type shell and tube designs, plate and frame designs, plate-fin designs, bare tube designs, and finned-tube designs. The performance efficiency of the variety of heat exchangers varies considerably and is dependent upon a number of factors including the design of the heat exchanger, the amount and efficiency of the heat transfer surface area, the temperature at which the heat exchanger is operating, and the fluids involved in the heat transfer process.
One approach to increase a heat exchanger's overall heat transfer rate is to increase the heat transfer surface by attachment of radial or longitudinal fins to the external surface of a heat exchanger tube. The art is filled with patents directed to finned-tube heat exchangers, and methods of using and making such finned-tube heat exchangers.
U.S. Pat. No. 4,901,667, issued Feb. 20, 1990 to Demetri discloses a gas-to-liquid heat exchanger formed by winding circular finned tubing into a helical coil having bare tubing wrapped around the coil such that it nests between adjacent turns of the finned tubing. Fittings at the inlets and outlets of both coils distribute the liquid stream so that a portion flows through each coil. The fan tube coil acts as a cooled baffle which directs the hot gas stream flowing over the finned tubes so that it contacts a greater portion of the finned tube external surface area at high velocity and increases the heat transfer effectiveness.
U.S. Pat. No. 5,472,047, issued Dec. 5, 1995 to Welkey discloses a heat exchanger tube bundle design for a shell and tube exchanger that eliminates the need for tube supports or baffles within a heat exchanger tube bundle. The Welkey tube bundle configuration uses a combination of bare tubes and longitudinally finned tubes positioned such that the longitudinal fins act as spacing and supporting means within the tube bundle. The longitudinal fins provide spacing and support substantially along the entire length of the tubes within the bundle and thereby eliminate the need for internal spacing or supporting means.
U.S. Pat. No. 5,848,638, issued Dec. 15, 1998 to Kim discloses a finned tube heat exchanger described therein as having a simple structure and increased heat exchanging performance. The heat exchanger has a plurality of fin plates spaced at regular intervals and arranged in parallel with one another, and a plurality of heat exchanger tubes extending through the fin plates and including a refrigerant fluid therein. Each of the fin plates has a plurality of strips projected from the surface thereof, and the strips include first to fifth rows of strips arranged between openings, which are disposed adjacent to one another, in a parallel relationship. The first row of strips is located near a leading edge of the fin plates and formed of two louverlike strips in a form of a trapezoid having a long side located on the upper stream of the air flow. Each of the second to fourth rows of strips is formed of one bridgelike strip in a form of a rectangle. The fifth row of strips is formed of two louverlike strips in a form of a trapezoid having a short side located on the upper stream of the air flow
U.S. Pat. No. 6,659,170, issued Dec. 9, 2003 to Kale discloses a finned-coil heat exchanger having a housing with spaced walls defining an internal chamber with air flowing from an upstream end to a downstream end, spaced transfer tubes with heat conducting media flowing therein from the downstream chamber end to the upstream chamber end, a series of spaced fins in contact with the tubes to transfer heat to flowing air, and a fan unit to move air through the exchanger. An air inlet is defined at the upstream end of the housing or in the lower end of one of the walls so that air can enter the internal chamber. The tubes each extend tortuously back and forth on a plane parallel to the direction of air flow so that there is a counterflow effect across the various segments of each tube. The tubes have at least six segments extending transversely across air flow with the tubes and fins being sized and spaced to provide for better air flow through the heat exchanger housing.
U.S. Pat. No. 6,662,858, issued Dec. 16, 2003 to Wang discloses a counter flow heat exchanger with integrated fins and tubes comprising metal plates overlapping with each other. Each of the metal plates has multiple elongated ridges spacing apart from each other. Adjacent metal plates oppositely overlap with each other such that the ridges in pairs form horizontal tubes and multiple connecting tubes on the plates form vertical tubes. Fluid inside the heat exchanger flows counter to external air allowing heat exchange to be reached effectively.
U.S. Pat. No. 6,789,317, issued Sep. 14, 2004 to Sohal et al., discloses a system for and method of manufacturing a finned tube for a heat exchanger. A continuous fin strip is provided with at least one pair of vortex generators. A tube is rotated and linearly displaced while the continuous fin strip with vortex generators is spirally wrapped around the tube.
U.S. Pat. No. 6,928,833, issued Aug. 16, 2005 to Watanabe et al., discloses a heat exchanger finned tube for use in fabricating a heat exchanger useful as the evaporator for refrigerators or the like wherein a hydrocarbon refrigerant is used. Two tube insertion holes spaced apart from each other are formed in each of plate fins and two straight tube portions of a hairpin tube are inserted through the respective holes of each plate fin to arrange the plate fins in parallel into a plurality of fin groups spaced apart on the straight tube portions longitudinally thereof. The hairpin tube is enlarged with use of a fluid to fixedly fit the plate fins of each tin group around an enlarged tube portion of the hairpin tube and provide a finless part between each pair of adjacent fin groups on each of the straight tube portions. The heat exchanger fabricated using the finned tube exhibits the desired refrigeration performance with the leakage of refrigerant diminished.